In "sighting in" firearms such as rifles, handguns, shotguns, muzzle loaders, machine guns and cannons, for example, it is necessary to adjust the sights of the firearm at a pre-established angle with the bore of the barrel of the gun or firearm where the angle is determined by the distance from the muzzle of the firearm to the target, and by the trajectory of the bullet or projectile fired by the firearm. In its most basic form, this was accomplished by mounting the firearm on a fixed stand or in a fixed position relative to a sighting-in target. In the past, the target was placed at the actual final desired distance from the firearm; and the test shot was fired. The point on the target where the bullet or projectile entered the target then was aligned with the sights (whether iron sights or a telescope sight). After this was done, a second shot was fired, and the procedure was repeated until the point of entry of the bullet or projectile aligned with the cross hairs or cross points of the sights. In many cases, a number of shots needed to be fired in order to effect the sighting in procedure.
For each different range or target distance, a separate sighting in procedure needed to be followed. Obviously, a significant amount of ammunition needed to be expended simply to sight in the firearm; and the sighting in needed to be effected in a place where the firing of the actual bullet or projectile from the firearm over the desired distance could be safely effected. The result was a relatively time consuming, costly and potentially dangerous sighting in technique.
U.S. Pat. No. 4,825,258 is directed to a device for sighting in rifles and similar firearms, without requiring the expenditure of several rounds of ammunition to effect the sighting in operation. The apparatus of this patent consists of a mounting assembly formed as a body of revolution and having a head portion, a mandrel portion, and a cylinder portion including an expansion tube or expandable arbor. The expandable arbor is inserted into the muzzle end of the gun bore, and is secured in an axial position; so that it aligns with the central axis of the gun bore. A light spot generating device is mounted in axial alignment with the mounting assembly head portion and the mandrel; so that a light beam projected to a distant target provides a sighting reference for an associated scope or mechanical sight on the rifle.
Another type of bore sighter has a mandrel or arbor, which is inserted into the muzzle end of the bore of the rifle. A bore sighter with grid lines in it is mounted in an offset position on the arbor, in alignment with the scope or sights of the rifle. Once all of these parts have been secured together, the rifle is placed on a suitable fixed support; and the reticle of the telescopic sights of the rifle are aligned with the cross hairs of a graduated reticle in the bore sighter. The particular alignment is made in accordance with the indication on the grid for the desired range. Once this has been done, sighting in by means of the firing and adjusting of live ammunition is effected to make the final adjustments. Once the final adjustments are made, the bore sighter once again is mounted on the rifle by inserting the arbor or mandrel into the end of the muzzle; and the recorded reticle position, where the cross hairs of the telescopic sight align with the graduated grid reticle in the bore sighter, is made for future reference. Using the scope adjustments, correction for bullet drop at a specific distance, provided the trajectory of a specific load is known, can be made. Each graduation on the bore sighter grid is equivalent to a particular drop at one hundred yards. Consequently, when the scope reticle is below the grid center, the gun will shoot high to compensate for the drop or trajectory of the load.
Some types of sighting devices employ a laser beam or light beam mounted on the firearm sights; so that the beam indicates the alignment of the sights vis a vis the target. U.S. patents directed to this technique are the patents to Vogel U.S. Pat. No. 5,031,349; Idan U.S. Pat. No. 4,665,622; Snyder U.S. Pat. No. 4,295,289; Snyder U.S. Pat. No. 4,079,534.
Other techniques have been employed for projecting a light through the gun barrel or firearm bore. The light is directed toward a target and is viewed through the firearm sight. Azimuth and elevation adjustments then are made in order to bring the projected light and the sight adjustments into proper alignment. A relatively complex device for accomplishing this purpose is described in the patent to Cameron U.S. Pat. No. 5,060,391. This device employs an optical assembly, a beam splitter, and an illumination source in an enclosure. The illumination source is used to provide a visible light, which is directed by the beam splitter into the firearm bore, which is illuminated from the muzzle to the chamber. This illumination is viewed through the firearm optical sight; and the proper adjustments are made to bring the images of the muzzle and chamber into coincident alignment. When this is accomplished, the cross hair of the firearm optical sight is adjusted to bring the cross hair into alignment with the muzzle, bore and chamber images.
Another patent to Edwards U.S. Pat. No. 3,734,627 discloses an apparatus for aligning aircraft guns using a laser. The laser is mounted in a gun barrel; and the laser beam is used to locate a reference point for determining the adjustments needed in aligning the guns with respect to the gun sight. The device of this patent is not readily adaptable to hand-held firearms of various calibers.
In the U.S. patent to Lanning U.S. Pat. No. 4,481,561, a flashlight is used for bore sighting with a long-barrelled shotgun or rifle. The flashlight itself includes a cartridge case, with an ejector rim and a primer opening in the base, and a sidewall defining an open front end. A battery and light bulb are located within the case; and a switch pin is placed in the primer opening to complete the circuit for illuminating the bulb. When the breech of the gun is closed, a spring coupled with the switch pin is moved to energize the light bulb.
It is desirable to provide a simple bore sighting device and method, which provides accurate bore sighting, using a device capable of utilization with a range of firearms of different calibers, and which quickly and effectively facilitates the bore sighting adjustments of the sights on the firearm.